Extractor



EXTRACTOR David L. Conger, Middle Haddam, Conn. Application December 6,1955, Serial No. 551,378 2 Claims. (Cl. 81-71) This invention relates toan improved twist extractor for use in removing threaded parts such aspipes, screws, and plugs which have been broken off in the aperture inwhich they are threaded. The removal of the broken part is accomplishedby inserting the extractor, which has longitudinally disposed ribs, inan aperture in or provided in the broken part and then turning theextractor in a direction opposite the direction of the thread of thepart. As the tool is thus turned, the ribs thereon will engage thebroken part and permit its removal.

Twist extractors heretofore available all too often have the tendency toeither ream the part desired to be removed or to expand the part duringthe removal process with the result that the purpose of the tool may bedefeated. It is an aim of this invention to provide a twist extractor ofnovel structure to eliminate any tendency of the extractor to ream orcut and which will, with a high efficiency, transfer to the part beingremoved the torque applied to the extractor thus precluding any but anegligible expansion of the part during the removal process.

It is another aim of this invention to provide a twist extractor of thetype described which may be used to remove threaded parts of a diametersubstantially less than the diameter heretofore considered as theminimum diameter of a part to which a twist extractor could besuccessfully applied.

It is still further an aim of this invention to provide an improvedextractor, as described, which will be more economical to manufacturethan existing extractors yet which will be equal or superior in strengthand service life.

Other objects will in part be obvious, and in part pointed out more indetail hereinafter.

The invention accordingly consists in the features of construction,combination of elements and arrangement of parts which will beexemplified in the construction hereafter set forth and the scope of theapplication of which will be indicated in the appended claims.

In the drawings: v

Fig. 1 is a side view of a twist extractor constructed in accordancewith this invention;

Fig. 2. is an end view of the extractor of Fig. 1;

Fig. 3 is a side view of the extractor of Fig. l rotated approximately90 from the position shown in Fig. 1;

Fig. 4 is a side view of a blank from which the ex tractor of Fig. 1 maybe fabricated; and

Fig. 5 is an end view of the blank of Fig. 4.

With reference to the drawings, and particularly Figs. 4 and 5, a twistextractor constructed in accordance with the invention is fabricatedfrom a blank having a wrench engageable head or shank 11 and a taperedbody or working portion 12. The cross section of the shank 11 may, ofcourse, be of any cross section which is suitable for the application ofa wrench during the use of the tool. The tapered blank is preferabyformed by forging in the interests of economy and strength; however, ofcourse, the blank may be formed by milling the body or ite States PatentWorking portion 12 from bar stock having the desired cross section ofthe shank. The working portion 12 is provided with a triangular crosssection producing at its juncture with the shank, the largest trianglewhich can be contained within the cross section of the shank, and thusutilizes to the maximum the strength and stock available in the shank.

As can be seen from Fig. 4, and as will be more fully explained, each ofthe sides 14 of the blank 10 are, in accordance with the invention,tapered from the shank 11 towards the nose 13 of the blank at an angleof approximately 3 /2 degrees. To complete the extractor, the blank is,preferably, heated to forging temperature either in a furnace or byinduction heating and the shank is gripped in the jaws of an air vise orchuck with the nose 13 held stationary. The shank is then rotated slowlythrough an angle of approximately 240 degrees to form the lands or ribs16. During the twisting. it is preferable to progressively chill theblank from the nose 13 toward the shank, such as by the localapplication of compressed air, to prevent the twist from beingconcentrated at the smallest cross section adjacent the nose. As will behereinafter more fully explained, the degree of twist given to the pieceis also critical. The resulting extractor is then heat treated toproduce a finished part.

It has been found that it is not necessary and in fact is preferable notto provide a sharp edge on the ribs 16 as during the use of the tool asharp cutting edge is not required to bite into the part to be removedin order for the tool to properly grip the part being removed. As

will be apparent hereinafter, the cross section of the tool lends itselfto optimum transfer of torque to the part being removed without tendingto ream the part and, in fact, even the application of an excess oftorque to the tool will not force it through the part being removed.

It is preferred that the twist imparted to the blank results in thelands or ribs 16 describing a spiral, the slope of which increases fromthe nose 13 to the approximate mid-point of the body or work portion 12.The provision of such an increasing spiral results in an extractorhaving a rapid initial draw-in with a subsequent increase in thetransfer of torque to the part. This, of course, is a distinctimprovement over either an extractor having a spiral providingrapiddraw-in but lacking desired torque transferring characteristics oran extractor which has the desired torque transferring characteristicsbut which has to be forced into the the removal process.

It should be apparent from the description of the method of fabricatingthe extractor that there are at least two distinct improvements in anextractor of this novel construction over presently availableextractors. First, the cross section of the body 12 taken at any pointalong its length is an equilateral triangle to assure that all three ofthe lands or ribs 16 of the finished extractor will be in engagementwith the part to be removed when the extractor is placed in the aperturein or provided in the part. In the use of conventional extractors havingmore than three sides, one or more of the lands or ribs thereon willmany times not be in engagement with the piece to be removed as theaperture in which the tool is placed is often not a true circle. As thislack of con-centricity of the aperture in the part to be removed willnot effect the engagement of the lands or ribs 16 of an extractorconstructed in accordance with the invention, the force applied to theextractor will be more evenly transferred to the piece to be removed,thus equalizing the stresses within the extractor as well as providing amore efficient transfer of torque to the threaded part.

Secondly, it should be apparent that it is not necessary to mill orotherwise provide grooves between the lands or ribs of the extractorprior to or subsequent to the twistpart, such as by hammering, to begining of the body portion. It is a particular advantage that when anextractor is constructed as described above, the grooves or flutes 17will be formed during the twisting of the blank 10, to thus eliminate acostly step in the manufacture of the item.

As heretofore mentioned, it has been determined that the taper of thesides 14 and the amount of twist applied to the blank is most critical.Although the reasons therefor are not completely understood, it has beenfound that if an extractor is constructed from a blank having atriangular cross section and sides 14 tapering at an angle of 3 /2degrees which blank is then axially twisted 240 degrees, the result willbe an extractor having the desired characteristics or producing only anegligible amount of expansion and no reaming of the threaded partduring the removal thereof by the extractor. It is possible to deviateslightly from the optimum values of taper and twist cited either byproportionately decreasing the taper and increasing the twist orincreasing the taper and decreasing the twist. However, any substantialdeviation will not produce the greatly improved results obtained by theuse of the critical values cited inasmuch as too great a taper willresult in an extractor having a length which is too short to be usefulover a reasonable range of aperture diameters; while too little taperwill result in an extractor which will bottom in shallow apertures.Also, too great a twist will cause the extractor to tear the piece whiletoo little twist will result in the extractor being unable to properlygrip the piece. Thus, it can be seen that if the taper is decreased andthe twist increased there is a ten dency for the extractor to bottom inshallow holes and also to tear the part being removed, while if thetaper is increased and the twist decreased, the resulting extractor isundesirably short and has a tendency to slip. It has been further foundthat it is possible to fabricate a twist extractor in accordance withthe invention which may be used to remove parts so small that anaperture of of an inch is the largest aperture permissible in the partwhere heretofore it was not considered possible to fabricate a twistextractor which would remove a part this small.

Thus, it can be seen that there has been provided a twist extractorwhich has all of the characteristics desired in such a tool whileeliminating all of the undesired characteristics. Its structure issimple and by comparison with presently available extractors,exceedingly economical to manufacture. It is, however, of ruggedconstruction so that such an extractor may be fabricated for use withparts provided with an axial aperture of as small as of an inch and willwithstand very severe treatment without fracture even after long periodsof use.

As many changes could be made in the above construe tion and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the followingclaims is intended to cover all of the generic and specific features ofthe invention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

i. claim:

1. in a twist extractor, a wrench engageable shank portion, a workingportion extending axially of said shank and having a triangular crosssection, and a plurality of work engaging ribs on said working portionformed by the juncture of adjacent sides of said working portion, saidworking portion having a twist whereby said ribs are disposed in aspiral, the slope of said spiral increasing from the end of said ribsopposite said shank to the approximate longitudinal mid-point of saidworking portion.

2. In a twist extractor, a Wrench engageable shank portion and a workingportion extending axially of said shank and having a triangular crosssection, one end of said working portion being angularly displacedapproximately 240 degrees from the other end thereof whereby three workengaging ribs disposed in a spiral are formed by the juncture ofadjacent sides of said working portion, said spiral having a slope whichincreases from the ends of said ribs opposite said shank to theapproximate longitudinal mid-point of said working portion, each of thesides of said Working portion being tapered approximately 3 /2 degreesfrom the juncture of said shank and said working portion as measuredwhen the ends of said working portion are in untwisted alignment.

References Cited in the file of this patent UNITED STATES PATENTS1,038,692 Walker Sept. 17, 1912 1,105,535 Roberts July 28, 19141,108,059 Zihler Aug. 18, 1914 1,160,706 Fowler Nov. 16, 1915 1,863,045Randall et al. June 14, 1932

